A single celled organism could accomplish the task faster but both could do it. When cells reproduce by mitosis or meiosis the DNA is copied from a single cell. Using a complex interaction of mRNA and many specific proteins and enzymes new cells are reproduced. Single celled organisms usually use asexual reproduction, this just means that they can reproduce all by themselves without the assistance of other cells. If a cell reproduces sexually, it must have the help and assistance of other very similar cells. Cells that are composed of like genetic material. This is why different animals can't reproduce offspring, the genetic material is different and therefore incompatible.

If by better suited you mean faster speed and higher success rate of genetic transformation, then it's the organism composed of a single cell that is better suited. New gene only needs to be inserted into one cell in the organism, and when the organism reproduces the DNA gets copied (because single-celled organisms usually use asexual reproduction) the new genetic material is reproduced. It takes longer for the multicellular organisms to have a total genetic transformation.

I don't know how to properly explain it but it's pretty much self-explanatory...